This is an amended application for first efficacy trial of a psychosocial intervention to treat Attention Deficit Hyperactivity Disorder (ADHD) in adults. This will be the principal investigator's first independent R01, hence meeting the NIH guidelines for the new investigator designation. The psychosocial intervention is based on our successful pilot study and on current conceptual models of adult ADHD. It is a cognitive-behavioral treatment targeting symptoms of ADHD in adults who remain symptomatic after adequate and stable medication treatment. Ten years of study by our research team and others - including controlled studies of stimulant medications and open studies of tricyclic, monoamine oxidase inhibitor, and atypical antidepressants - reveal that 20-50% of adults are considered nonresponders to psychopharmacotherapy due to insufficient symptom reduction or inability [unreadable] to tolerate side-effects. Moreover, adults who do respond to treatment typically show a reduction in only [unreadable] 50% or fewer of the core symptoms of ADHD. This leaves pharmacologically-treated patients with residual symptoms which cause significant distress and functional impairment. The current application builds on our pilot work, which followed NIMH guidelines for completing stages of psychosocial intervention development necessary before proposing an (R01) efficacy trial. We conceptualized the novel intervention based on theories of ADHD and cognitive behavioral therapy, developed and standardized a CBT treatment manual with expert consultation, and provided evidence for its feasibility, patient acceptability, and clinical utility by conducting a pilot randomized controlled trial of the CBT compared to maintenance psychopharmacology alone. The goal of the pilot was to estimate [unreadable] the effect size of the CBT intervention (versus attempting to find statistically significant improvement in such a small sample). Results revealed large effect sizes that reached clinical and statistical significance. Patients in the CBT condition had greater reductions in global severity as well as in core ADHD symptoms. Endpoints were ratings by a blinded independent assessor and patient self-report data. We propose to build on this work by conducting an adequately-powered efficacy study comparing [unreadable] CBT to a credible, placebo-control psychotherapy. [unreadable] [unreadable]